FIG. 1A is directed towards a prior art servo combo driver diagram 100 for a HDD. The diagram 100 includes a shock sensor 110 having a shock sensor 115. The shock sensor 115 has a resonance frequency, which can lay outside of a normal shock signal range. However, a shock has elements of an impulse that resonates at the resonance frequency, thereby creating at least in part a false signal that needs to be accounted for through employment of a notch filter.
FIG. 1Bi is directed towards illustrating an example frequency response of the shock sensor 115. As is illustrated, the shock sensor 115 has a resonance frequency, which can be both within a desired sensor range and outside of a sensor range. However, a shock has elements of an impulse that resonates at the resonance frequency, thereby creating at least in part a false signal that needs to be accounted for through employment of a notch filter.
FIG. 1Bii is directed towards an example prior art shock sensor transient response. As is illustrated, the resonance frequencies are propagated.
The periodic nature of the resonance is determined from the physical structure of the sensor, so when the physical structure (or X, Y, Z sizes) of the sensor varies, the resonance frequency also varies. For one typical sensor used in HDD drive, the resonance frequency is roughly times order of the shock signal (1˜3 k Hz signal, 20 k˜50 kHz resonance), and the resonance gain is about 30 dB more of the shock signal. Once the sensor receives shock (or hit by something), the shock and resonance signals are input to an IC as the summation of the signals. Both shock signal and resonance signals gradually decays back to zero.
One such example is given in U.S. Pat. No. 8,132,459 to Toga, et al. (“Toga,”) entitled “System and Method to Determine Mechanical Resonance of an Accelerometer”, hereby incorporated by reference in its entirety. Generally, in Toga, an “electric impulse” is applied to a shock sensor at different frequencies to determine a resonance of the shock sensor, so a notch filter for this resonance can then be applied. However, the “electric impulse” approach can require a number of incremental changes to the notch frequency in order to determine the correct notch filter frequency. Generally, Toga is directed to the generation of the mechanical resonance frequency of a shock sensor by electrically stimulating the sensor.
FIG. 1Ci comparison of an actual behavior of a shock sensor between a mechanical hammer and an electrical impulse. Mechanical hammer: the sensor or the peripheral is mechanically (actually) hit and outputs both the shock and resonance signal. Electrical Impulse: Toga patent for electrically stimulating the sensor and the sensor outputs only the resonance signal.
FIG. 1Cii discloses how, as seen on the impulse and mechanical waveforms, the resonance signal amplitudes generated by impulses decay as time passes, and eventually comes back to steady state.
Generally, Toga uses the electrical impulse approach to generate or pull out the mechanical resonance of a shock sensor. Toga also uses ‘zero crossing’ of the resonance signal with respect to the reference voltage so that it catches and digitize the resonance signal and it can be measured as a ‘time’, which can be converted to the frequency (=1/time). However, it does not talk about how to calibrate the notch filter into the resonance frequency. Furthermore, according to Toga, even if it can find the resonance frequency, the notch filter needs absolute tolerance on the frequency settings as it only finds the input frequency.
Therefore, there is a need in the art to address at least some of the issues associated with prior art notch filters for HDDs.